"Latent thiol mercaptan chain transfer agent," as used herein, is defined as compounds containing at least one thiol group and at least one protected thiol group. During use in a polymerization, the at least one thiol group reacts with a polymer chain being formed from at least one first ethylenically unsaturated monomer. This yields a polymer chain containing at least one protected thiol group, primarily at the terminal portion of the chain. This polymer formed can be used as is, or can be reacted further.
The term "latent" refers to the fact that the protected thiol group does not react with the first ethylenically unsaturated monomer or monomers, but after the polymerization is conducted, the protected thiol group can be deprotected, for example by a cleaving reaction, to yield a terminal thiol group on the polymer chain. These terminal thiol groups can then react further, for example with at least one second ethylenically unsaturated monomer, forming a block copolymer.
"Block copolymers" as used herein are defined as the "linear" macromolecules formed by attachment of different polymers or copolymers at their ends. The term linear as used herein, includes molecules which are perfectly linear and also those bearing side chains but are still predominantly linear. Due to the ability to chemically combine unlike polymeric segments in one molecule, block copolymers have unique properties, making them particularly useful for their surface active properties, such as for example in stabilizing physical blends of otherwise incompatible polymeric or monomeric compounds.
The block copolymer products of the present invention can be used directly in water-based emulsion coatings, elastomers, adhesives, caulks and mastics. Still further uses for these copolymers are as plastic additives for use as compatibilizers of polymer-polymer blends.